An optical block is an assembly comprising a source of light, a reflector, and a front glass. Such an assembly may either be capable of being disassembled, or else it may be sealed and incapable of being disassembled (American standards). To mount such a block on a motor vehicle and pointing in a suitable direction, it is conventional to provide the optical block with positioning tabs, and in particular with orientation tabs.
The constitution of one such optical block is, for example, defined in U.S. standard SAE J 571. This standard is entitled "Dimensional Specifications for Sealed Beam Headlamp Unit" and provides definitions both for round optical blocks and for rectangular optical blocks, and in particular it defines mounting positions together with means for obtaining correct positioning of the block relative to the vehicle.
For example, a seven inch round optical block has three positioning tabs disposed around its periphery, extending parallel to its optical axis, and located at successive angles of 130.degree., 130.degree., and 100.degree., with one of the tabs being at 70.degree. from the upper vertical axis of the lamp unit, and with all these specifications being defined by the standard to which reference is now made.
In more general terms, the present invention applies to any optical block having positioning tabs, regardless of whether the optical block is of the sealed type and therefore conforms exactly with said U.S. standards, or whether the optical block is of the European type in which only the external shape and the location of the positioning tabs are standardized, or else, more generally still, the optical block has positioning tabs or lugs somewhere around its periphery.
In order to mount such an optical block on a motor vehicle, proposals have already been made to use a rear shell constituted by an annular portion of a sphere having an open end (zone), the contour of the shell being approximately identical to that of the reflector of the optical block, being engaged therewith, and bearing there against by means of a peripheral flange constituted by the rear part of the rim of the glass. The assembly is held together by means of a front retaining ring covering the front part of said glass rim and coming into contact with the flange of said shell. The front retaining ring and the rear shell are fixed to each other by means of screws. When the screws are tightened, the glass rim of the optical block is clamped between the front retaining ring and the rear shell.
In order to position the optical block correctly, the positioning tabs of the optical block are engaged in corresponding notches provided for this purpose in the shell.
For a full understanding of the above description, reference may be made to said U.S. standard SAE J 571 which defines the retaining ring and the mounting notches.
Finally, in order to adjustably fix the assembly constituted in this way on a motor vehicle, the shell is generally provided with fixing lugs which are integrally manufactured therewith.
It can be seen that such mounting makes use of two main parts, namely: the front retaining ring and the rear shell, together with a set of screws for interconnecting said two main parts. As a result the materials and labor costs are relatively high and it would be advantageous to be able to reduce them.
To this end, the present invention seeks to provide a device for fixing an optical block of the above-mentioned type and for adjusting its position, with the device being constituted by a one-piece support which is advantageously constituted by a plastic molding.